Physical activity decreases the risk of cardiovascular disease, Type 2 Diabetes, and multiple cancers, and is important for obesity prevention. US children's active commuting to school (ACS; walking or cycling to school), previously common (42% in 1969-1970) is now uncommon (13% in 2009). This decline coincided with the obesity epidemic, which disproportionately affects low-income and ethnic minority children. Programs to increase children's moderate-to-vigorous physical activity (MVPA) and lower obesity risk are necessary. The Bicycle Train is an innovative program in which children cycle to and from school led by adults. The Bicycle Trains provide another option for ACS, especially for children who live too far to walk to school. No randomized controlled trials (RCT) have evaluated Bicycle Trains and children's ACS or MVPA. Increasing the percent of children who cycle to school is sub-objective PA-14 of US Healthy People 2020. The Primary Goals are to (a) conduct a pilot cluster RCT of a Bicycle Train program among low- income, ethnic minority 4th and 5th grade children and (b) collect concurrent accelerometer and GPS data and validate algorithms to identify and measure physical activity intensity and duration for children's cycling compared to heart rate monitors. This pilot study will provide feasibility data and extend the validity of quantifying cycling-related MVPA for a future fully-powered R01-funded Bicycle Train cluster RCT. Our Specific Aims will be to: SA1) evaluate among 80 4th and 5th grade ethnic minority children the feasibility of a pilot cluster RCT of a Bicycle Train program for (a) recruiting participants for a planned full-scale cluster RCT (b) promoting their participation, and (c) identifying barriers/facilitators to their participation; and SA2) validate algorithms examining concurrent accelerometry and GPS data to identify and measure children's physical activity intensity and duration while cycling compared to the criterion standards of heart rate monitoring and direct observation Feasibility Criteria: As recommended for pilot studies, in which the main goal is to test feasibility of a research protocol, a fully powered R01-funded cluster RCT will be determined to be feasible if: FC 1) We successfully recruit 80 low-income 4th and 5th grade children for the pilot Bicycle Train cluster RCT FC 2) The intervention children participate in the Bicycle Train program on average twice/week FC 3) Algorithms analyzing concurrent GPS and accelerometer data have at least moderate agreement with heart rate data in distinguishing children's cycling-related physical activity duration and intensity from other physical activities and riding in a motor vehicle This R21 application will provide important planning and methods validation targeted towards ethnic- minority children, the population at highest risk for childhood obesity in the US.